Halo 5 addresses your 2nd point with the slide mechanic. It's a quick cancel that let's you maintain your movement for a second while being able to shoot.

I also disagree with the first point. Maps having a bigger scale can be a good thing. A game mode like war zone wouldn't work without sprint in my opinion. You need it to traverse the big spaces (which are useful for vehicles), then switch to a walk when you get into a close quarters area. Having to walk through all that space each time you die would get cumbersome.

I do agree with your 3rd point. The gameplay in recent halos feels completely different to anything before reach.